The present invention relates to the field of cathode ray display tubes, such as are used in high ambient lighting areas, such as for aircraft cockpit displays. In such applications it is critical to optimize the display contrast by minimizing glare and light reflections which impair the viewer's readability.
It has long been the practice to use clear glass and increase the signal brightness to higher luminance levels than the reflected light. More recently it has become the practice to use low light transmissivity faceplate glass in such tubes to reduce the reflection of exterior light from the interior surface of the faceplate, and from the phosphor disposed on the faceplate interior surface. Incident light is effectively absorbed by the low light transmissivity faceplate glass. Anti-reflective coatings have also been used on the faceplate exterior surface to reduce reflected incident light which lowers contrast. Circular polarizers have also been used with the tube faceplate to reduce specular reflections from the faceplate interior surface.
The conventional cathode ray display tube typically has an exterior surface which is planar or convex with respect to the viewer. With a planar or convex faceplate, objects in front of the faceplate which emit or reflect light cause specular reflections which can result in disturbing glare for the viewer and loss of contrast for the display.
In the typical high ambient light level applications, such as aircraft cockpit use, the viewer is typically in a fixed position relatively close to the tube faceplate.